Recent years have seen increasing demand for miniaturization and increased reliability of dielectric elements as electronic circuits reach higher densities. Miniaturization of electronic components such as laminated ceramic capacitors, together with increased capacity and higher reliability are rapidly progressing, while the applications thereof are also expanding. Various characteristics are required as these applications expand. Materials having barium titanate (BaTiO3) as the main component are often conventionally used as dielectric compositions.
For example, a smoothing capacitor or a snubber capacitor such as a motor vehicle DC-DC converter or AC-DC inverter is often used in a location in which a high DC bias of several hundred volts is applied.
There is therefore a problem with conventional electronic components having a dielectric layer comprising a dielectric composition which has BaTiO3 as the main component in that there is a reduction in dielectric constant when a high DC bias is applied. This problem is due to the fact that BaTiO3 is a ferroelectric material, so the dielectric constant tends to decrease the higher the DC bias. When electronic components having a dielectric layer comprising a dielectric composition which has BaTiO3 as the main component are used for applications involving high DC bias application it is therefore necessary to devise a method for using such electronic components, for example. According to one example of a known method, the amount of reduction in the dielectric constant is anticipated and a plurality of the electronic components is connected in parallel for use in order to maintain the required capacitance or dielectric constant.
Furthermore, in a conventional dielectric composition having BaTiO3 as the main component, the field intensity applied to the dielectric layer is small during use under a low DC bias such as several volts or less, so the thickness of the dielectric layers can be set to a sufficiently thin level that breakdown does not occur. This means that there are essentially no problems such as short circuiting defects which occur as a result of breakdown of the dielectric layer. However, reductions in insulation resistance and short circuiting defects etc. caused by the dielectric composition itself become a problem during use under a high DC bias such as several hundred volts or greater. The dielectric composition forming the dielectric layer therefore needs to be extremely reliable.
In the prior art, dielectric compositions having improved reliability have been developed by adding a paraelectric such as barium zirconate. However, even greater reliability has become desirable in recent years.
Japanese Patent Application JP 2000-223351 A describes a laminated ceramic capacitor in which the temperature characteristics, dielectric constant and high-temperature load lifespan are improved by setting a specific range for the surface area ratio of a core and a shell in dielectric ceramic particles having a core-shell structure.
However, the improvement in high-temperature load lifespan is inadequate with the laminated ceramic capacitor described in Japanese Patent Application JP 2000-223351 A and further improvements are needed.
Furthermore, Japanese Patent Application JP 2005-22891 A mentioned below describes a dielectric porcelain comprising perovskite barium titanate crystal grains in which part of the B site of BaTiO3, which is a ferroelectric material, is substituted with Zr (BTZ-type crystal grains), and likewise comprising perovskite bismuth sodium titanate crystal grains (BNST-type crystal grains). In that dielectric porcelain, Mg, Mn and at least one rare earth element are present in the grain boundary phase between the BTZ-type crystal grains and the BNST-type crystal grains. In addition, the dielectric porcelain has a core-shell structure in which the mean particle size of both the BTZ-type crystal grains and the BNST-type crystal grains is 0.3-1.0 μm.
However, with the dielectric porcelain and laminated ceramic capacitor described in Japanese Patent Application JP 2005-22891 A, there is a large reduction in dielectric constant with respect to DC bias and the dielectric constant cannot be considered adequate for use under a high voltage, for instance in a smoothing capacitor or a snubber capacitor such as a motor vehicle DC-DC converter or AC-DC inverter. Further improvement in the dielectric constant when a DC bias is applied is therefore needed.